This invention relates to a shield that surrounds a section of an automatic transmission adjacent to the transmissions's large rotating components and that contains fragments created by breakage of a rotating component. More particularly, this invention relates to a shield that includes a strengthened fluid pan and a rigid metal plate jacket that conforms to a section of the exterior surface of the transmission and mounts directly to the strengthened fluid pan.
Automatic transmissions manufactured for conventional automobiles can catastrophically fail when used in race cars. Large rotating components are both the fastest moving and highest stressed components of the transmission and consequently are frequently a source of dangerous transmission failures. Rotating components of an automatic transmission rotate about a transmission axis that extends through the transmission along a driveline direction of the transmission. Breakage of a large rotating component can create fragments that are propelled in a direction radially away from the transmission axis by the momentum of the rotating component. Those fragments can break other parts of the transmission creating additional fragments and openings that provide a path for fast-moving fragments to escape. Such fragments can injure the driver and others and can be sharp enough to puncture tires of the race car. Further, fluid escaping from the transmission through holes created by fragments can coat the race car's tires or the race track causing loss of traction. Both tire punctures and loss of traction can cause the race car to be difficult to control and possibly cause an accident.
Automatic transmissions typically have a housing surrounding the rotating components and a fluid pan mounted to an underside of the housing adjacent to the large rotating components. Fluid pans having greater volume and made from stronger materials than conventional automatic transmission fluid pans are used in race cars to increase the volume of fluid available to the transmission and provide increased cooling of transmission fluid. These fluid pans typically provide increased fluid capacity compared to conventional fluid pans by extending farther below the transmission housing than conventional fluid pans, thereby decreasing clearance between the fluid pan and ground below the transmission. They also provide increased resistance to penetration by fragments compared to conventional fluid pans.
In addition to strengthened fluid pans, shields are placed adjacent to the section of the transmission surrounding large rotating components to prevent fragments from escaping from the transmission at high speed. These shields increase the safety of the race car at a cost of increased difficulty of maintenance of the transmission. Two types of shields have been used to prevent fragments from an automatic transmission from creating a safety hazard. One is a flexible "blanket" shield that is wrapped around an exterior surface of the housing and fluid pan. The other type is a rigid jacket shield that is a formed metal plate that generally conforms to the housing and is positioned closely adjacent to an exterior surface of the housing adjacent to large rotating components of the transmission. These types of shield provide different degrees of protection and present different disadvantages.
A blanket shield is continuous flexible shield that completely surrounds the section of the exterior of the automatic transmission adjacent to large rotating components. A blanket shields generally wraps around on itself to assure containment of all fragments and accommodate some variation in installation of the blanket shield and shape of the transmission and connections to the transmission. They include mounting straps that are secured to the transmission or engine to prevent the blanket shield from sliding away from the transmission. Blanket shields are cumbersome and can interfere with exterior connections of the transmission, such as cooling lines and shift linkage. Further, they surround the fluid pan and inhibit cooling of fluid in the fluid pan. Installation of a blanket shield can be time consuming because of the necessity of assuring that the blanket does not interfere with the various connections to the transmission.
Jacket shields are conventionally a metal plate that is formed to closely conform to the section of the exterior surface of the transmission housing adjacent to the large rotating components. Jacket shields have connection access holes and borders that are shaped to allow connections to the transmission without interference with the plate shield. A jacket shield must be mounted to the transmission to accurately position the access holes and borders adjacent the locations of transmission connections. Jacket shields are typically mounted to the transmission housing by attaching brackets to the housing using one or two fluid pan mounting holes on two sides of the housing and bolting the shield to the brackets. Straps are positioned closely adjacent to the fluid pan and connected to the brackets o the sides of the transmission housing to assure that the jacket plate shield will remain adjacent to the rotating components of the transmission in the event that the brackets become separated from the housing.
Jacket shields avoid interference with connections to a transmission, do not significantly interfere with heat transfer through the fluid pan, and are generally easier to install than blanket shields. However, they are not an ideal solution for the problems of either safety or ease of installation. Jacket shields do not surround the fluid pan. The jacket shield conventionally extends around the transmission housing from locations on opposing sides of the transmission that are adjacent to and slightly separated from fluid pan mounting sections of the transmission. The jacket shield protects the driver and others from fragments that may be ejected through the housing of the transmission, but does not provide protection from fragments that may eject through the fluid pan.
Use of a strengthened fluid pan with a jacket shield improves protection at the underside of the transmission. Strengthened and enlarged fluid pans require that brackets and straps that secure a jacket shield to the transmission accommodate a range of sizes of fluid pans. Brackets either have several pieces that must be assembled to position straps close to the fluid pan, or position straps away from the fluid pan potentially allowing movement of the shield. At a minimum, the brackets and straps include several pieces that must be assembled and increase the time required to assemble the transmission and shield. Further, the strengthened fluid pan and jacket shield do not provide a continuous shield surrounding the rotating components of the transmission. The fluid pan is held in place by the conventional fluid pan mounting, usually several bolts. The jacket shield is held in place by the brackets connected to the housing by a small number of fluid pan mounting bolts. This assembly does not provide direct connection between the jacket shield and the strengthened fluid pan and consequently does not provided a continuous shield that can resist separation at all locations around the axis of the rotating components of the automatic transmission.
A need therefore exists for a shield for an automatic transmission that: provides protection from ejection of fragments created by breakage of a rotating component of an automatic transmission at all locations radially adjacent to the rotating components; will resist separation at all locations around the rotating components; and does not interfere with connections to the automatic transmission. In addition, the need also exists for a shield that can be quickly assembled and mounted to an automatic transmission. The need further exists for a fluid pan for an automatic transmission that provides increased volume compared to conventional fluid pans without extending an unacceptable distance from the housing of the transmission and that enhances cooling of the fluid within the fluid pan.